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{{Short description|Computing using molecular biology hardware}}
[[File:DNA orbit animated.gif|thumb|The biocompatible computing device: Deoxyribonucleic acid (DNA)]]
'''DNA computing''' is an emerging branch of [[unconventional computing]] which uses [[DNA]], [[biochemistry]], and [[molecular biology]] hardware, instead of the traditional [[electronic computing]]. Research and development in this area concerns theory, experiments, and applications of DNA computing. Although the field originally started with the demonstration of a computing application by [[Leonard Adleman|Len Adleman]] in 1994, it has now been expanded to several other avenues such as the development of storage technologies,<ref name=":7">{{Cite journal|last1=Church|first1=G. M.|last2=Gao|first2=Y.|last3=Kosuri|first3=S.|date=2012-08-16|title=Next-Generation Digital Information Storage in DNA|journal=Science|volume=337|issue=6102|pages=1628|doi=10.1126/science.1226355|pmid=22903519|bibcode=2012Sci...337.1628C|s2cid=934617|issn=0036-8075|doi-access=free|pmc=3581509}}</ref><ref>{{Cite journal|last1=Erlich|first1=Yaniv|last2=Zielinski|first2=Dina|date=2017-03-02|title=DNA Fountain enables a robust and efficient storage architecture|journal=Science|volume=355|issue=6328|pages=950–954|doi=10.1126/science.aaj2038|pmid=28254941|bibcode=2017Sci...355..950E|s2cid=13470340|issn=0036-8075|url=https://zenodo.org/record/889697}}</ref><ref>{{Cite journal|last1=Organick|first1=Lee|last2=Ang|first2=Siena Dumas|last3=Chen|first3=Yuan-Jyue|last4=Lopez|first4=Randolph|last5=Yekhanin|first5=Sergey|last6=Makarychev|first6=Konstantin|last7=Racz|first7=Miklos Z.|last8=Kamath|first8=Govinda|last9=Gopalan|first9=Parikshit|last10=Nguyen|first10=Bichlien|last11=Takahashi|first11=Christopher N.|date=March 2018|title=Random access in large-scale DNA data storage|url=https://www.nature.com/articles/nbt.4079|journal=Nature Biotechnology|language=en|volume=36|issue=3|pages=242–248|doi=10.1038/nbt.4079|pmid=29457795|s2cid=205285821|issn=1546-1696|url-access=subscription}}</ref> nanoscale imaging modalities,<ref>{{Cite journal|last1=Shah|first1=Shalin|last2=Dubey|first2=Abhishek K.|last3=Reif|first3=John|date=2019-04-10|title=Programming Temporal DNA Barcodes for Single-Molecule Fingerprinting|journal=Nano Letters|volume=19|issue=4|pages=2668–2673|doi=10.1021/acs.nanolett.9b00590|pmid=30896178|bibcode=2019NanoL..19.2668S|s2cid=84841635|issn=1530-6984}}</ref><ref>{{Cite journal|last1=Sharonov|first1=Alexey|last2=Hochstrasser|first2=Robin M.|date=2006-12-12|title=Wide-field subdiffraction imaging by accumulated binding of diffusing probes|journal=Proceedings of the National Academy of Sciences|language=en|volume=103|issue=50|pages=18911–18916|doi=10.1073/pnas.0609643104|issn=0027-8424|pmid=17142314|pmc=1748151|bibcode=2006PNAS..10318911S|doi-access=free}}</ref><ref name=":8">{{Cite journal|last1=Jungmann|first1=Ralf|last2=Avendaño|first2=Maier S.|last3=Dai|first3=Mingjie|last4=Woehrstein|first4=Johannes B.|last5=Agasti|first5=Sarit S.|last6=Feiger|first6=Zachary|last7=Rodal|first7=Avital|last8=Yin|first8=Peng|date=May 2016|title=Quantitative super-resolution imaging with qPAINT|journal=Nature Methods|language=en|volume=13|issue=5|pages=439–442|doi=10.1038/nmeth.3804|pmid=27018580|pmc=4941813|issn=1548-7105}}</ref> synthetic controllers and reaction networks,<ref name=":0">{{Cite journal|last1=Shah|first1=Shalin|last2=Wee|first2=Jasmine|last3=Song|first3=Tianqi|last4=Ceze|first4=Luis|last5=Strauss|first5=Karin|author5-link=Karin Strauss|last6=Chen|first6=Yuan-Jyue|last7=Reif|first7=John|date=2020-05-04|title=Using Strand Displacing Polymerase To Program Chemical Reaction Networks|journal=Journal of the American Chemical Society|volume=142|issue=21|pages=9587–9593|doi=10.1021/jacs.0c02240|pmid=32364723|s2cid=218504535|issn=0002-7863}}</ref><ref name=":1">{{Cite journal|last1=Chen|first1=Yuan-Jyue|last2=Dalchau|first2=Neil|last3=Srinivas|first3=Niranjan|last4=Phillips|first4=Andrew|last5=Cardelli|first5=Luca|last6=Soloveichik|first6=David|last7=Seelig|first7=Georg|date=October 2013|title=Programmable chemical controllers made from DNA|journal=Nature Nanotechnology|language=en|volume=8|issue=10|pages=755–762|doi=10.1038/nnano.2013.189|pmid=24077029|pmc=4150546|bibcode=2013NatNa...8..755C|issn=1748-3395}}</ref><ref name=":2">{{Cite journal|last1=Srinivas|first1=Niranjan|last2=Parkin|first2=James|last3=Seelig|first3=Georg|last4=Winfree|first4=Erik|last5=Soloveichik|first5=David|date=2017-12-15|title=Enzyme-free nucleic acid dynamical systems|journal=Science|language=en|volume=358|issue=6369|pages=eaal2052|doi=10.1126/science.aal2052|issn=0036-8075|pmid=29242317|doi-access=free}}</ref><ref name=":3">{{Cite journal|last1=Soloveichik|first1=David|last2=Seelig|first2=Georg|last3=Winfree|first3=Erik|date=2010-03-23|title=DNA as a universal substrate for chemical kinetics|journal=Proceedings of the National Academy of Sciences|language=en|volume=107|issue=12|pages=5393–5398|doi=10.1073/pnas.0909380107|issn=0027-8424|pmid=20203007|pmc=2851759|bibcode=2010PNAS..107.5393S|doi-access=free}}</ref> etc.
 
== History ==
== A brief history of DNA computing and molecular programming ==
[[Leonard Adleman]] of the [[University of Southern California]] initially developed this field in 1994.<ref name=":11">{{Cite journal | last1 = Adleman | first1 = L. M. | title = Molecular computation of solutions to combinatorial problems | doi = 10.1126/science.7973651 | journal = Science | volume = 266 | issue = 5187 | pages = 1021–1024 | year = 1994 | pmid = 7973651| bibcode = 1994Sci...266.1021A | citeseerx = 10.1.1.54.2565 }} &mdash; The first DNA computing paper. Describes a solution for the directed [[Hamiltonian path problem]]. Also available here: {{cite web |url= http://www.usc.edu/dept/molecular-science/papers/fp-sci94.pdf |title= Archived copy |access-date= 2005-11-21 |url-status= dead |archive-url= https://web.archive.org/web/20050206144827/http://www.usc.edu/dept/molecular-science/papers/fp-sci94.pdf |archive-date= 2005-02-06 }}</ref> Adleman demonstrated a [[proof-of-concept]] use of DNA as a form of computation which solved the seven-point [[Hamiltonian path problem]]. Since the initial Adleman experiments, advances have occurred and various [[Turing machine]]s have been proven to be constructible.<ref>{{Cite journal | last1 = Boneh | first1 = D. | last2 = Dunworth | doi = 10.1016/S0166-218X(96)00058-3 | first2 = C. | last3 = Lipton | first3 = R. J. | last4 = Sgall | first4 = J. Í. | title = On the computational power of DNA | journal = Discrete Applied Mathematics | volume = 71 | issue = 1–3 | pages = 79–94 | year = 1996 | doi-access = free }} &mdash; Describes a solution for the [[booleanBoolean satisfiability problem]]. Also available here: {{cite web |url= http://www.cs.tau.ac.il/~kempe/TEACHING/SEMINAR-LENS-SPRING08/boneh95DNAcomputational.pdf |title= Archived copy |access-date=2011-10-14 |url-status= dead |archive-url= https://web.archive.org/web/20120406103849/http://www.cs.tau.ac.il/~kempe/TEACHING/SEMINAR-LENS-SPRING08/boneh95DNAcomputational.pdf |archive-date= 2012-04-06 }}
</ref><ref>{{cite journal |author1= Lila Kari |author2= Greg Gloor |author3= Sheng Yu | date= January 2000 | title = Using DNA to solve the Bounded Post Correspondence Problem |url=http://citeseer.ist.psu.edu/kari00using.html |journal = Theoretical Computer Science | volume = 231 | issue = 2 | pages = 192&ndash;203 | url = http://citeseer.ist.psu.edu/kari00using.html | doi=10.1016/s0304-3975(99)00100-0 | doi-access = free }} &mdash; Describes a solution for the bounded [[Post correspondence problem]], a hard-on-average NP-complete problem. Also available here: [http://www.csd.uwo.ca/~lila/pdfs/Using%20DNA%20to%20solve%20the%20Bounded%20Post%20Correspondence%20Problem.pdf]</ref>
 
Since then the field has expanded into several avenues. In 1995, the idea for DNA-based memory was proposed by Eric Baum<ref>{{Cite journal|last=Baum|first=E. B.|date=1995-04-28|title=Building an associative memory vastly larger than the brain|journal=Science|language=en|volume=268|issue=5210|pages=583–585|doi=10.1126/science.7725109|issn=0036-8075|pmid=7725109|bibcode=1995Sci...268..583B|doi-access=free}}</ref> who conjectured that a vast amount of data can be stored in a tiny amount of DNA due to its ultra-high density. This expanded the horizon of DNA computing into the realm of memory technology although the ''in vitro'' demonstrations were made almost after almost a decade.
 
The field of DNA computing can be categorized as a sub-field of the broader [[DNA nanotechnology|DNA nanoscience]] field started by [http://seemanlab4.chem.nyu.edu/ Ned Seeman] about a decade before Len Adleman's demonstration.<ref>{{Cite journal|last=Seeman|first=Nadrian C.|date=1982-11-21|title=Nucleic acid junctions and lattices|journal=Journal of Theoretical Biology|language=en|volume=99|issue=2|pages=237–247|doi=10.1016/0022-5193(82)90002-9|pmid=6188926|bibcode=1982JThBi..99..237S|issn=0022-5193}}</ref> Ned's original idea in the 1980s was to build arbitrary structures using bottom-up DNA self-assembly for applications in crystallography. However, it morphed into the field of structural DNA self-assembly<ref>{{Cite journal|last1=Tikhomirov|first1=Grigory|last2=Petersen|first2=Philip|last3=Qian|first3=Lulu|date=December 2017|title=Fractal assembly of micrometre-scale DNA origami arrays with arbitrary patterns|url=https://www.nature.com/articles/nature24655|journal=Nature|language=en|volume=552|issue=7683|pages=67–71|doi=10.1038/nature24655|pmid=29219965|bibcode=2017Natur.552...67T|s2cid=4455780|issn=1476-4687|url-access=subscription}}</ref><ref>{{Cite journal|last1=Wagenbauer|first1=Klaus F.|last2=Sigl|first2=Christian|last3=Dietz|first3=Hendrik|date=December 2017|title=Gigadalton-scale shape-programmable DNA assemblies|url=https://www.nature.com/articles/nature24651|journal=Nature|language=en|volume=552|issue=7683|pages=78–83|doi=10.1038/nature24651|pmid=29219966|bibcode=2017Natur.552...78W|s2cid=205262182|issn=1476-4687|url-access=subscription}}</ref><ref>{{Cite journal|last1=Ong|first1=Luvena L.|last2=Hanikel|first2=Nikita|last3=Yaghi|first3=Omar K.|last4=Grun|first4=Casey|last5=Strauss|first5=Maximilian T.|last6=Bron|first6=Patrick|last7=Lai-Kee-Him|first7=Josephine|last8=Schueder|first8=Florian|last9=Wang|first9=Bei|last10=Wang|first10=Pengfei|last11=Kishi|first11=Jocelyn Y.|date=December 2017|title=Programmable self-assembly of three-dimensional nanostructures from 10,000 unique components|journal=Nature|language=en|volume=552|issue=7683|pages=72–77|doi=10.1038/nature24648|pmid=29219968|pmc=5786436|bibcode=2017Natur.552...72O|issn=1476-4687}}</ref> which as of 2020 is extremely sophisticated. Self-assembled structure from a few nanometers tall all the way up to several tens of micrometers in size have been demonstrated in 2018.
 
In 1994, Prof. Seeman's group demonstrated early DNA lattice structures using a small set of DNA components. While the demonstration by Adleman showed the possibility of DNA-based computers, the DNA design was trivial because as the number of nodes in a graph grows, the number of DNA components required in Adleman's implementation would grow exponentially. Therefore, computer scientistscientists and biochemists started exploring tile-assembly where the goal was to use a small set of DNA strands as tiles to perform arbitrary computations upon growth. Other avenues that were theoretically explored in the late 90's include DNA-based security and cryptography,<ref>{{Cite journal|last1=Leier|first1=André|last2=Richter|first2=Christoph|last3=Banzhaf|first3=Wolfgang|last4=Rauhe|first4=Hilmar|date=2000-06-01|title=Cryptography with DNA binary strands|url=http://www.sciencedirect.com/science/article/pii/S0303264700000836|journal=Biosystems|language=en|volume=57|issue=1|pages=13–22|doi=10.1016/S0303-2647(00)00083-6|pmid=10963862|bibcode=2000BiSys..57...13L |issn=0303-2647|url-access=subscription}}</ref> computational capacity of DNA systems,<ref>{{Cite journal|last1=Guarnieri|first1=Frank|last2=Fliss|first2=Makiko|last3=Bancroft|first3=Carter|date=1996-07-12|title=Making DNA Add|url=https://www.science.org/doi/10.1126/science.273.5272.220|journal=Science|language=en|volume=273|issue=5272|pages=220–223|doi=10.1126/science.273.5272.220|issn=0036-8075|pmid=8662501|bibcode=1996Sci...273..220G|s2cid=6051207|url-access=subscription}}</ref> DNA memories and disks,<ref>{{Cite journal|last1=Bancroft|first1=Carter|last2=Bowler|first2=Timothy|last3=Bloom|first3=Brian|last4=Clelland|first4=Catherine Taylor|date=2001-09-07|title=Long-Term Storage of Information in DNA|url=https://www.science.org/doi/10.1126/science.293.5536.1763c|journal=Science|language=en|volume=293|issue=5536|pages=1763–1765|doi=10.1126/science.293.5536.1763c|pmid=11556362|s2cid=34699434|issn=0036-8075|url-access=subscription}}</ref> and DNA-based robotics.<ref name=":10">{{Cite journal|last1=Yin|first1=Peng|last2=Yan|first2=Hao|last3=Daniell|first3=Xiaoju G.|last4=Turberfield|first4=Andrew J.|last5=Reif|first5=John H.|date=2004|title=A Unidirectional DNA Walker That Moves Autonomously along a Track|journal=Angewandte Chemie International Edition|volume=43|issue=37|pages=4906–4911|doi=10.1002/anie.200460522|pmid=15372637|bibcode=2004ACIE...43.4906Y |issn=1521-3773}}</ref>
 
Before 2002, [[Lila Kari]] showed that the DNA operations performed by genetic recombination in some organisms are Turing complete.<ref name=bucke>{{citation|url=http://communications.uwo.ca/com/western_news/profiles/biocomputing_researcher_awarded_the_bucke_prize_20020321435998/ |title=Biocomputing researcher awarded the Bucke Prize |journal=Western News |publisher=[[University of Western Ontario]] |date=March 21, 2002}}</ref>
In 2003, [https://users.cs.duke.edu/~reif/ John Reif's group] first demonstrated the idea of a DNA-based walker that traversed along a track similar to a line follower robot. They used molecular biology as a source of energy for the walker. Since this first demonstration, a wide variety of DNA-based walkers have been demonstrated.
 
In 2003, [https://users.cs.duke.edu/~reif/ John Reif's group] first demonstrated the idea of a DNA-based walker that traversed along a track similar to a line follower robot. They used molecular biology as a source of energy for the walker. Since this first demonstration, a wide variety of DNA-based walkers have been demonstrated.
 
== Applications, examples, and recent developments ==
In 1994 [[Leonard Adleman]] presented the first prototype of a DNA computer. The [[:de:TT-100|TT-100]] was a test tube filled with 100 microliters of a DNA solution. He managed to solve an instance of the directed [[Hamiltonian path]] problem.<ref>Braich, Ravinderjit S., et al. "Solution of a satisfiability problem on a gel-based DNA computer." ''DNA Computing''. Springer Berlin Heidelberg, 2001. 27-42.</ref> In Adleman's experiment, the Hamiltonian Path Problem was implemented notationally as the "[[travelling salesman problem]]". For this purpose, different DNA fragments were created, each one of them representing a city that had to be visited. Every one of these fragments is capable of a linkage with the other fragments created. These DNA fragments were produced and mixed in a [[test tube]]. Within seconds, the small fragments form bigger ones, representing the different travel routes. Through a chemical reaction, the DNA fragments representing the longer routes were eliminated. The remains are the solution to the problem, but overall, the experiment lasted a week.<ref>{{cite journal | last1 = Adleman | first1 = Leonard M | year = 1998 | title = Computing with DNA | journal = Scientific American | volume = 279 | issue = 2| pages = 54–61 | doi = 10.1038/scientificamerican0898-54 | bibcode = 1998SciAm.279b..54A }}</ref> However, current technical limitations prevent the evaluation of the results. Therefore, the experiment isn't suitable for the application, but it is nevertheless a [[proof of concept]].
 
=== Combinatorial problems ===
First results to these problems were obtained by [[Leonard Adleman]].
 
* In 1994: Solving a [[Hamiltonian path problem|Hamiltonian path]] in a graph with 7seven summits.
* In 2002: Solving a [[NP-complete]] problem as well as a [[3-satisfiability|3-SAT]] problem with 20 variables.
 
=== Tic-tac-toe game ===
In 2002, J. Macdonald, D. StefanovicStefanović and M. StojanovicStojanović created a DNA computer able to play [[tic-tac-toe]] against a human player.<ref>[FR] - J. Macdonald, D. Stefanovic et M. Stojanovic, ''Des assemblages d'ADN rompus au jeu et au travail'', [[:fr:Pour la Science|Pour la Science]], {{n°|No.&nbsp;375}}, January 2009, {{p.|68-75}}</ref> The calculator consists of nine bins corresponding to the nine squares of the game. Each bin contains a substrate and various combinations of DNA enzymes. The substrate itself is composed of a DNA strand onto which was grafted a fluorescent chemical group at one end, and the other end, a repressor group. Fluorescence is only active if the molecules of the substrate are cut in half. The DNA enzymes simulate [[Logic function|logical functions]]. For example, such a DNA will unfold if two specific types of DNA strand are introduced to reproduce the logic function AND.
 
By default, the computer is considered to have played first in the central square. The human player starts with eight different types of DNA strands corresponding to the eight remaining boxes that may be played. To play box number i, the human player pours into all bins the strands corresponding to input #i. These strands bind to certain DNA enzymes present in the bins, resulting, in one of these bins, in the deformation of the DNA enzymes which binds to the substrate and cuts it. The corresponding bin becomes fluorescent, indicating which box is being played by the DNA computer. The DNA enzymes are divided among the bins in such a way as to ensure that the best the human player can achieve is a draw, as in real tic-tac-toe.
 
=== Neural network based computing ===
Kevin Cherry and [[Lulu Qian]] at Caltech developed a DNA-based artificial neural network that can recognize 100-bit hand-written digits. They achieveachieved this by programming on a computer in advance with the appropriate set of weights represented by varying concentrations weight molecules which willare later be added to the test tube that holds the input DNA strands.<ref>{{Cite journal|last1=Qian|first1=Lulu|last2=Winfree|first2=Erik|last3=Bruck|first3=Jehoshua|date=July 2011|title=Neural network computation with DNA strand displacement cascades|journal=Nature|language=En|volume=475|issue=7356|pages=368–372|doi=10.1038/nature10262|pmid=21776082|s2cid=1735584|issn=0028-0836}}</ref><ref name=":4">{{Cite journal|last1=Cherry|first1=Kevin M.|last2=Qian|first2=Lulu|date=2018-07-04|title=Scaling up molecular pattern recognition with DNA-based winner-take-all neural networks|journal=Nature|language=En|volume=559|issue=7714|pages=370–376|doi=10.1038/s41586-018-0289-6|pmid=29973727|issn=0028-0836|bibcode=2018Natur.559..370C|s2cid=49566504|url=https://authors.library.caltech.edu/84840/}}</ref>
 
=== Improved speed with Localized (cache-like) Computing ===
One of the challenges of DNA computing is its slow speed. While DNA asis a substrate is biologically compatible substrate, i.e., it can be used at places where silicon technology cannot, its computationcomputational speed is still very slow. For example, the square-root circuit used as a benchmark in the field tooktakes over 100 hours to complete.<ref name=":5">{{Cite journal|last1=Qian|first1=L.|last2=Winfree|first2=E.|s2cid=10053541|date=2011-06-02|title=Scaling Up Digital Circuit Computation with DNA Strand Displacement Cascades|journal=Science|volume=332|issue=6034|pages=1196–1201|doi=10.1126/science.1200520|pmid=21636773|issn=0036-8075|bibcode=2011Sci...332.1196Q}}</ref> While newer ways with external enzyme sources are reporting faster and more compact circuits,<ref name=":6">{{Cite journal|last1=Song|first1=Tianqi|last2=Eshra|first2=Abeer|last3=Shah|first3=Shalin|last4=Bui|first4=Hieu|last5=Fu|first5=Daniel|last6=Yang|first6=Ming|last7=Mokhtar|first7=Reem|last8=Reif|first8=John|date=2019-09-23|title=Fast and compact DNA logic circuits based on single-stranded gates using strand-displacing polymerase|journal=Nature Nanotechnology|volume=14|issue=11|pages=1075–1081|doi=10.1038/s41565-019-0544-5|pmid=31548688|issn=1748-3387|bibcode=2019NatNa..14.1075S|s2cid=202729100}}</ref> Chatterjee et al. demonstrated an interesting idea in the field to speedupspeed up computation through localized DNA circuits.,<ref name="spacearch">{{Cite journal|last1=Chatterjee|first1=Gourab|last2=Dalchau|first2=Neil|last3=Muscat|first3=Richard A.|last4=Phillips|first4=Andrew|last5=Seelig|first5=Georg|date=2017-07-24|title=A spatially localized architecture for fast and modular DNA computing|journal=Nature Nanotechnology|volume=12|issue=9|pages=920–927|doi=10.1038/nnano.2017.127|pmid=28737747|issn=1748-3387|bibcode=2017NatNa..12..920C}}</ref> Thisa concept is being further explored by other groups.<ref name=":9">{{Cite journal|last1=Bui|first1=Hieu|last2=Shah|first2=Shalin|last3=Mokhtar|first3=Reem|last4=Song|first4=Tianqi|last5=Garg|first5=Sudhanshu|last6=Reif|first6=John|date=2018-01-25|title=Localized DNA Hybridization Chain Reactions on DNA Origami|journal=ACS Nano|volume=12|issue=2|pages=1146–1155|doi=10.1021/acsnano.7b06699|pmid=29357217|issn=1936-0851}}</ref> This idea, while originally proposed in the field of computer architecture, has been adopted in this field as well. In computer architecture, it is very well-known that if the instructions are executed in sequence, having them loaded in the cache will inevitably lead to fast performance, also called as the principle of localization. This is because with instructions in fast cache memory, there is no need swap them in and out of main memory, which can be slow.<ref name="spacearch"/> Similarly, in [https://www.nature.com/articles/nnano.2017.127 localized DNA computing], the DNA strands responsible for computation are fixed on a breadboard -like substrate ensuring physical proximity of the computing gates. Such localized DNA computing techniques have been shown to potentially reduce the computation time by [https://www.nature.com/articles/nnano.2017.127 orders of magnitude].<ref name="spacearch"/>
 
=== Renewable (or reversible) DNA computing ===
Subsequent research on DNA computing has produced [https://ieeexplore.ieee.org/document/8642913 reversible DNA computing], bringing the technology one step closer to the silicon-based computing used in (for example) [[Personal computer|PC]]s. In particular, [https://web.archive.org/web/20190201104419/https://users.cs.duke.edu/~reif/index.htm John Reif] and his group at Duke University have proposed two different techniques to reuse the computing DNA complexes. The first design uses dsDNA gates,<ref>{{Cite journal|last1= Garg|first1= Sudhanshu|last2= Shah|first2= Shalin|last3= Bui|first3= Hieu|last4= Song|first4= Tianqi|last5= Mokhtar|first5= Reem|last6= Reif|first6= John|date= 2018|title= Renewable Time-Responsive DNA Circuits|journal= Small|language= en|volume= 14|issue= 33|pages= 1801470|doi= 10.1002/smll.201801470|pmid= 30022600|bibcode= 2018Small..1401470G|issn= 1613-6829|doi-access= free}}</ref> while the second design uses DNA hairpin complexes.<ref>
{{Cite journal
|last1= Eshra|first1= A.|last2= Shah|first2= S.
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|date= 2019
|title= Renewable DNA hairpin-based logic circuits
|journal= [[IEEE Transactions on Nanotechnology]]
|volume= 18|pages= 252–259
|doi= 10.1109/TNANO.2019.2896189|issn= 1536-125X
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|bibcode= 2019ITNan..18..252E|s2cid= 5616325}}
</ref>
While both the designs face some issues (such as reaction leaks), this appears to represent a significant breakthrough in the field of DNA computing. Some other groups have also attempted to address the gate reusability problem.<ref>{{Cite journal|last1=Song|first1=Xin|last2=Eshra|first2=Abeer|last3=Dwyer|first3=Chris|last4=Reif|first4=John|date=2017-05-25|title=Renewable DNA seesaw logic circuits enabled by photoregulation of toehold-mediated strand displacement|journal=RSC Advances|language=en|volume=7|issue=45|pages=28130–28144|doi=10.1039/C7RA02607B|bibcode=2017RSCAd...728130S|issn=2046-2069|doi-access=free}}</ref><ref>{{Cite journalbook|last1=Goel|first1=Ashish|last2=Ibrahimi|first2=Morteza|chapter=Renewable, Time-Responsive DNA Logic Gates for Scalable Digital Circuits |date=2009|editor-last=Deaton|editor-first=Russell|editor2-last=Suyama|editor2-first=Akira|title=Renewable, Time-Responsive DNA Logic Gates for Scalable Digital Circuits|journal=DNA Computing and Molecular Programming|series=Lecture Notes in Computer Science|volume=5877|language=en|___location=Berlin, Heidelberg|publisher=Springer|pages=67–77|doi=10.1007/978-3-642-10604-0_7|isbn=978-3-642-10604-0}}</ref>
 
Using strand displacement reactions (SRDs), reversible proposals are presented in [https://www.mdpi.com/2073-8994/13/7/1242the "Synthesis Strategy of Reversible Circuits on DNA Computers" paper] <ref>{{Cite journal|last1=Rofail|first1=Mirna|last2=Younes|first2=Ahmed|date=July 2021|title=Synthesis Strategy of Reversible Circuits on DNA Computers|journal=Symmetry|language=en|volume=13|issue=7|pages=1242|doi=10.3390/sym13071242|bibcode=2021Symm...13.1242R|doi-access=free}}</ref> for implementing reversible gates and circuits on DNA computers by combining DNA computing and reversible computing techniques. This paper also proposes a universal reversible gate library (URGL) for synthesizing n-bit reversible circuits on DNA computers with an average length and cost of the constructed circuits better than the previous methods.<ref>{{Cite journal|last1=Rofail|first1=Mirna|last2=Younes|first2=Ahmed|date=July 2021|title=Synthesis Strategy of Reversible Circuits on DNA Computers|journal=Symmetry|language=en|volume=13|issue=7|pages=1242|doi=10.3390/sym13071242|bibcode=2021Symm...13.1242R|doi-access=free}}</ref>
 
==Methods==
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The most fundamental operation in DNA computing and molecular programming is the strand displacement mechanism. Currently, there are two ways to perform strand displacement:
 
* [[Toehold mediated strand displacement]] (TMSD)<ref name=":5" />
* Polymerase-based strand displacement (PSD)<ref name=":0" />
 
=== Toehold exchange ===
BesideBesides simple strand displacement schemes, DNA computers have also been constructed using the concept of toehold exchange.<ref name=":4" /> In this system, an input DNA strand binds to a [[sticky end]], or toehold, on another DNA molecule, which allows it to displace another strand segment from the molecule. This allows the creation of modular logic components such as AND, OR, and NOT gates and signal amplifiers, which can be linked into arbitrarily large computers. This class of DNA computers does not require enzymes or any chemical capability of the DNA.<ref>{{Cite journal|last1=Seelig|first1=G.|last2=Soloveichik|first2=D.|last3=Zhang|first3=D. Y.|last4=Winfree|first4=E.|s2cid=10966324|date=8 December 2006|title=Enzyme-free nucleic acid logic circuits|journal=Science|volume=314|issue=5805|pages=1585–1588|bibcode=2006Sci...314.1585S|doi=10.1126/science.1132493|pmid=17158324|url=https://authors.library.caltech.edu/22753/2/DNA_logic_circuits2006_supp.pdf}}</ref>
 
=== Chemical reaction networks (CRNs) ===
The full stack for DNA computing looks very similar to a traditional computer architecture. At the highest level, a C-like general purpose programming language is expressed using a set of [[Chemical reaction networks|chemical reaction networks (CRNs)]]. This intermediate representation gets translated to ___domain-level DNA design and then implemented using a set of DNA strands. In 2010, [http://www.dna.caltech.edu/~winfree/ Erik Winfree's group] showed that DNA can be used as a substrate to implement arbitrary chemical reactions. This opened the way to design and synthesis of biochemical controllers since the expressive power of CRNs is equivalent to a Turing machine.<ref name=":0" /><ref name=":1" /><ref name=":2" /><ref name=":3" /> Such controllers can potentially be used ''in vivo'' for applications such as preventing hormonal imbalance.
 
===DNAzymes===
Catalytic DNA ([[deoxyribozyme]] or DNAzyme) catalyze a reaction when interacting with the appropriate input, such as a matching [[oligonucleotide]]. These DNAzymes are used to build logic gates analogous to digital logic in silicon; however, DNAzymes are limited to 1one-, 2two-, and 3three-input gates with no current implementation for evaluating statements in series.
 
The DNAzyme logic gate changes its structure when it binds to a matching oligonucleotide and the fluorogenic substrate it is bonded to is cleaved free. While other materials can be used, most models use a fluorescence-based substrate because it is very easy to detect, even at the single molecule limit.<ref name="weiss">
{{Cite journal | last1 = Weiss | first1 = S. | s2cid = 9697423 | title = Fluorescence Spectroscopy of Single Biomolecules | doi = 10.1126/science.283.5408.1676 | journal = Science | volume = 283 | issue = 5408 | pages = 1676–1683 | year = 1999 | pmid = 10073925|bibcode = 1999Sci...283.1676W }}. Also available here: http://www.lps.ens.fr/~vincent/smb/PDF/weiss-1.pdf
</ref> The amount of fluorescence can then be measured to tell whether or not a reaction took place. The DNAzyme that changes is then “used"used", and cannot initiate any more reactions. Because of this, these reactions take place in a device such as a continuous stirred-tank reactor, where old product is removed and new molecules added.
 
Two commonly used DNAzymes are named E6 and 8-17. These are popular because they allow cleaving of a substrate in any arbitrary ___location.<ref>
{{Cite journal | last1 = Santoro | first1 = S. W. | last2 = Joyce | first2 = G. F. |year=1997 |title = A general purpose RNA-cleaving DNA enzyme | doi = 10.1073/pnas.94.9.4262 | journal = Proceedings of the National Academy of Sciences | volume = 94 | issue = 9 | pages = 4262–4266 | year bibcode= 19971997PNAS...94.4262S | pmid doi=10.1073/pnas.94.9.4262 9113977| pmc =20710 20710|bibcode pmid= 1997PNAS...94.4262S9113977 | doi-access = free }}. Also available here: [http://www.pnas.org/content/94/9/4262.full.pdf]
</ref> Stojanovic and MacDonald have used the E6 DNAzymes to build the [[MAYA I]]<ref>
{{Cite journal | last1 = Stojanovic | first1 = M. N. | last2 = Stefanovic | first2 = D. | doi year= 10.1038/nbt8622003 | title = A deoxyribozyme-based molecular automaton | journal = Nature Biotechnology | volume = 21 | issue = 9 | pages = 1069–1074 | year doi= 200310.1038/nbt862 | pmid =12923549 12923549| s2cid = 184520 }}. Also available here: [https://web.archive.org/web/20120401132040/http://www.cs.duke.edu/courses/cps296.6/current/papers/SS03.pdf]
</ref> and [[MAYA II]]<ref>
{{Cite journal | last1 = MacDonald | first1 = J. | last2 = Li | first2 = Y. | last3 = Sutovic | first3 = M. | last4 = Lederman | first4 = H. | last5 = Pendri | first5 = K. | last6 = Lu | first6 = W. | last7 = Andrews | first7 = B. L. | last8 = Stefanovic | first8 = D. | last9 = Stojanovic | first9 = M. N. | doi year= 10.1021/nl06206842006 | title = Medium Scale Integration of Molecular Logic Gates in an Automaton | journal = Nano Letters | volume = 6 | issue = 11 | pages = 2598–2603 | year = 2006 | pmid = 17090098|bibcode = 2006NanoL...6.2598M |doi=10.1021/nl0620684 |pmid=17090098}}. Also available here: [http://www.ece.gatech.edu/research/labs/bwn/nanos/papers/Medium_Scale_Integration_of_Molecular.pdf]
</ref> machines, respectively; Stojanovic has also demonstrated logic gates using the 8-17 DNAzyme.<ref>
{{Cite journal | last1 = Stojanovic | first1 = M. N. | last2 = Mitchell | first2 = T. E. | last3 = Stefanovic | first3 = D. | doi year= 10.1021/ja016756v2002 | title = Deoxyribozyme-Based Logic Gates |url=https://figshare.com/articles/Deoxyribozyme-Based_Logic_Gates/3638808 |journal = Journal of the American Chemical Society | volume = 124 | issue = 14 | pages = 3555–3561 | year doi= 200210.1021/ja016756v | pmid = 11929243| url bibcode= https://figshare2002JAChS.com/articles/Deoxyribozyme-Based_Logic_Gates/3638808124.3555S }}. Also available at [http://www.dna.caltech.edu/courses/cs191/paperscs191/stojanovic_mitchell_stefanovic2002.pdf]
</ref> While these DNAzymes have been demonstrated to be useful for constructing logic gates, they are limited by the need forof a metal cofactor to function, such as Zn<sup>2+</sup> or Mn<sup>2+</sup>, and thus are not useful [[in vivo]].<ref name="weiss" /><ref>
{{Cite journal | last1 = Cruz | first1 = R. P. G. | last2 = Withers | first2 = J. B. | last3 = Li | first3 = Y. | title = Dinucleotide Junction Cleavage Versatility of 8-17 Deoxyribozyme | doi = 10.1016/j.chembiol.2003.12.012 | journal = Chemistry & Biology | volume = 11 | issue = 1 | pages = 57–67 | year = 2004 | pmid = 15112995| doi-access = free | hdl = 11375/23673 | hdl-access = free }}
</ref>
 
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| volume = 2 | issue = 4 | pages = 497–503 | url = http://www.wisdom.weizmann.ac.il/~udi/DNA5/scripps_short/index.htm | doi = 10.1098/rsfs.2011.0118| pmid = 22649583 | pmc = 3363030 | archive-url=https://web.archive.org/web/20090103224150/http://www.wisdom.weizmann.ac.il/~udi/DNA5/scripps_short/index.htm |archive-date=2009-01-03 | access-date = 2009-08-13 }}</ref>
Benenson, Shapiro and colleagues have demonstrated a DNA computer using the [[FokI]] enzyme<ref name="shapiro">{{Cite journal | last1 = Benenson | first1 = Y. | last2 = Paz-Elizur | first2 = T. | last3 = Adar | first3 = R. | last4 = Keinan | first4 = E. | last5 = Livneh | first5 = Z. | last6 = Shapiro | first6 = E. | doi year= 10.1038/351065332001 | title = Programmable and autonomous computing machine made of biomolecules | journal = Nature | volume = 414 | issue = 6862 | pages = 430–434 | year bibcode= 20012001Natur.414..430B | pmid doi=10.1038/35106533 11719800| pmc = 3838952| bibcode |pmid= 2001Natur.414..430B 11719800}}. Also available here: [http://www.technion.ac.il/~keinanj/pub/110.pdf] {{Webarchive|url=https://web.archive.org/web/20120510194658/http://www.technion.ac.il/~keinanj/pub/110.pdf |date=2012-05-10 }}</ref> and expanded on their work by going on to show automata that diagnose and react to [[prostate cancer]]: under expression of the genes [[PPAP2B]] and [[GSTP1]] and an over expression of [[PIM1]] and [[HPN (gene)|HPN]].<ref name="shapiro_cancer">{{Cite journal|last1=Benenson|first1=Y.|last2=Gil|first2=B.|last3=Ben-Dor|first3=U.|last4=Adar|first4=R.|last5=Shapiro|first5=E.|year=2004|title=An autonomous molecular computer for logical control of gene expression|journal=Nature|volume=429|issue=6990|pages=423–429|bibcode=2004Natur.429..423B|doi=10.1038/nature02551|pmc=3838955|pmid=15116117}}. Also available here: [https://web.archive.org/web/20131023055858/http://www.wisdom.weizmann.ac.il/~udi/papers/automoleculcomp_nat04.pdf An autonomous molecular computer for logical control of gene expression]</ref> Their automata evaluated the expression of each gene, one gene at a time, and on positive diagnosis then released a single strand DNA molecule (ssDNA) that is an antisense for [[MDM2]]. MDM2 is a repressor of [[p53|protein 53]], which itself is a tumor suppressor.<ref>
{{Cite journal | last1 = Bond | first1 = G. L. | last2 = Hu | first2 = W. | last3 = Levine | first3 = A. J. | doi = 10.2174/1568009053332627 | title = MDM2 is a Central Node in the p53 Pathway: 12 Years and Counting | journal = [[Current Cancer Drug Targets]] | volume = 5 | issue = 1 | pages = 3–8 | year = 2005 | pmid = 15720184}}
</ref> On negative diagnosis it was decided to release a suppressor of the positive diagnosis drug instead of doing nothing. A limitation of this implementation is that two separate automata are required, one to administer each drug. The entire process of evaluation until drug release took around an hour to complete. This method also requires transition molecules as well as the FokI enzyme to be present. The requirement for the FokI enzyme limits application ''in vivo'', at least for use in "cells of higher organisms".<ref name="kahan08">
{{Cite journal | last1 = Kahan | first1 = M. | last2 = Gil | first2 = B. | last3 = Adar | first3 = R. | last4 = Shapiro | first4 = E. |year=2008 |title = Towards molecular computers that operate in a biological environment | doi = 10.1016/j.physd.2008.01.027 | journal = Physica D: Nonlinear Phenomena | volume = 237 | issue = 9 | pages = 1165–1172 | year = 2008 |bibcode = 2008PhyD..237.1165K |doi=10.1016/j.physd.2008.01.027}}. Also available here: [http://www.ece.gatech.edu/research/labs/bwn/nanos/papers/Towards_molecular_computers_that_operate_in_a_biological_environment.pdf]
</ref> It should also be pointed out that the 'software' molecules can be reused in this case.
 
=== Algorithmic self-assembly ===
[[Image:Rothemund-DNA-SierpinskiGasket.jpg|thumb|300px|DNA arrays that display a representation of the [[Sierpinski gasket]] on their surfaces. Click the image for further details. Image from Rothemund ''et al.'', 2004.<ref name="rothemund04winfree" />]]
 
{{Main|DNA nanotechnology#Algorithmic self-assembly|l1 = DNA nanotechnology: Algorithmic self-assembly}}
 
DNA nanotechnology has been applied to the related field of DNA computing. DNA tiles can be designed to contain multiple sticky ends with sequences chosen so that they act as [[Wang tile]]s. A DX array has been demonstrated whose assembly encodes an [[Exclusive or|XOR]] operation; this allows the DNA array to implement a [[cellular automaton]] which generates a [[fractal]] called the [[Sierpinski gasket]]. This shows that computation can be incorporated into the assembly of DNA arrays, increasing its scope beyond simple periodic arrays.<!--
--><ref name="rothemund04winfree">{{Cite journal | last1 = Rothemund | first1 = P. W. K. | last2 = Papadakis | first2 = N. | last3 = Winfree | first3 = E. | doi = 10.1371/journal.pbio.0020424 | title = Algorithmic Self-Assembly of DNA Sierpinski Triangles | journal = PLOS Biology | volume = 2 | issue = 12 | pages = e424 | year = 2004 | pmid = 15583715| pmc =534809 | doi-access = free }}</ref>
 
== Capabilities ==
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== Alternative technologies ==
A partnership between [[IBM]] and [[Caltech]] was established in 2009 aiming at "[[DNA chip]]s" production.<ref>[http://media.caltech.edu/press_releases/13284](Caltech's own article) {{webarchive |url=https://web.archive.org/web/20111014075545/http://media.caltech.edu/press_releases/13284 |date=October 14, 2011 }}</ref> A Caltech group is working on the manufacturing of these nucleic-acid-based integrated circuits. One of these chips can compute whole square roots.<ref>[https://www.science.org/doi/full/10.1126/science.1200520 Scaling Up Digital Circuit Computation with DNA Strand Displacement Cascades]</ref> A compiler has been written in [[Perl]].<ref>[https://www.science.org/doi/abs/10.1126/science.1200520] Online</ref> in [[Perl]].
 
== Pros and cons ==
Line 125 ⟶ 127:
 
==See also==
{{colbegindiv col}} <!-- seems inhibited by the encroachment from above on the RHS -->
* [[Biocomputer]]
* [[Chemical computer]]
Line 139 ⟶ 141:
* [[Transcriptor]]
* [[Wetware computer]]
* [[Molecular logic gate]]
{{Div col end}}
 
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* [http://computer.howstuffworks.com/dna-computer.htm How Stuff Works explanation]
* Dirk de Pol: [https://unglaublich.de/dns-ein-neuer-supercomputer/ ''DNS – Ein neuer Supercomputer?'']. In: Die Neue Gesellschaft / Frankfurter Hefte {{ISSN|0177-6738}}, Heft 2/96, Februar 1996, S. 170–172
* [https://web.archive.org/web/20040825021955/http://physicsweb.org/article/news/6/3/11/ ‘DNA'DNA computer’computer' cracks code], Physics Web
* [http://archive.arstechnica.com/reviews/2q00/dna/dna-1.html Ars Technica]
* [https://www.nytimes.com/2004/04/29/science/29DNA.html - The New York Times DNA Computer for detecting Cancer]